With the increasing emphasis on productivity and flexibility of manufacturing operations, it has become more necessary to be able to quickly change the dies on a press line. A vehicle known as a die change truck, or simply as a die truck, is one means for speeding the die change process. The truck has a generally planar, horizontal die support bed which may be moved vertically up or down to the level of the press bed. Contained within slots in the bed are a pair of powered members or pusher bars which are moved toward and away from the press bed as hydraulic cylinders extend and retract, to either push a die toward a press bed or pull a die off a press bed. Clearly, some means is necessary for engaging the powered member with the die to be pushed or pulled.
Die change trucks are of two general types, front loading and side loading. In a front loading die truck, the die support bed is manuevered to a position flush with the press bed, and the die is pushed or pulled directly onto or off of the press bed. Clearly, in the front loading truck, the retracted powered members must be spaced back from the press bed a distance sufficient to allow the powered member to push the die onto the press bed in a single stroke or extension. If not, then it is clear that some additional spacing member would have to be interposed between the powered member and the die to obtain extra pushing length on a subsequent stroke. It is also clear that such a truck would have to be turned around in order to service presses located on the otherside of the truck.
Die trucks of the side loading type are designed to service presses in dual lines located on either side of the truck. In this type of truck, the powered member has a total length generally equal to the entire width of the die support bed, and will extend or retract in either direction out of the die support bed for only about half its length. The die support bed will have to be positioned level with, but spaced away from the press bed, because the powered members extend out to the press bed, and some other members, known as bridging members or bridging rails, will have to be interposed between the die support bed and the press bed to span the distance therebetween and provide a surface to move the die along. Also, the total stroke length available to either side of the press bed will unlikely be sufficient to move many dies onto or off of the press bed in a single stroke, and it will be necessary to retract the powered member, re-engage it with the die at a different point, and push or pull again in a subsequent stroke. Therefore, it is desirable that the means for engaging the powered member with the die be easily and quickly movable.
Prior art die engaging means consist generally of a heavy block with a pair of dowel pins which fit down into a line of holes spaced along the length of the powered member, known sometimes as a "pusher bar". The block engages an edge of the die to push it, or has a cable hooked around it in order to pull a die off of the press bed. These blocks must be physically pulled up out of the pin holes, and moved to different locations on the bar, an often difficult and time consuming task.